Catalysts are used, inter alia, for the oxidation of incompletely burned exhaust gas constituents, for example in the exhaust from internal combustion engines, as well as for the reduction of nitrogen oxides in such exhaust gases. The catalysts are made by depositing catalytically active components on a coating which in turn is deposited on a carrier material.
Platinum group metals, for example, are used as catalytically active components in such catalysts.
The coating is formulated to provide the largest possible active surface area. The large surface area necessary for receiving the catalytically active components is produced, according to the state of the art, with a metallic oxide, e.g., in the form of gamma Al.sub.2 O.sub.3, (see published German Specification DE-OS No. 32 23 500). It is also known that oxide whiskers can be formed on smooth metallic carrier foils which form an enlarged surface for anchoring an oxidic intermediary layer on which the catalytically active component is deposited (see British Pat. No. 2,062,723).
However, the known catalyst systems are relatively expensive. The cultivation of the whiskers requires special techniques during casting for a rapid hardening, in order to seed column crystals, and also requires a subsequent annealing in order to allow the columns to grow. These methods also require appropriate supports on the surface of which column crystals can be generated, such as Fe-Al-Cr alloys.